Instruments for checking and determining levels and differences in elevation for such jobs as hanging ceilings, leveling floors and walls, laying out building interiors, and the like are well known in the art. Perhaps the best known such device is the transit, which can be used to determine levels by providing a planar line of sight. The transit is set up so that the scope is rotatable in a horizontal plane. A first operator then sights through the transit, usually at a leveling rod and target, and instructs a second person to move the rod up or down on the desired surface until the target corresponds to the planar level sighted through the transit. Such a device is limited to applications where there is an uninterrupted line of sight between the elements which are to be leveled. A transit cannot be used where the surfaces which are to be leveled are in different rooms, for example, whereby walls prevent the transit from sighting both objects from a single location. Further, a transit requires at least two persons to operate: one to sight through the transit, and the other to man the leveling rod.
Accordingly, there is a need to provide a leveling instrument which can check and determine levels and differences in elevation which can be operated by a single person and independently of a continuous line of sight.
A more sophisticated apparatus for creating a plane for determining a proper level for hanging ceilings and the like consists of a rotating source of light such as a laser. By setting up the device so that the beam of light rotates in the desired plane, a horizontal line of light is reflected onto the surrounding surfaces corresponding to the desired level. Such devices suffer the aforementioned limitation requiring a continuous line of sight between the light source and the elements which are being leveled. Further, such devices are expensive and relatively delicate instruments which are ill-suited for many construction site environments.
Accordingly, there is a need to provide a leveling instrument which is rugged, inexpensive to manufacture, and requires no special skills on the part of the user.